The present invention generally relates to structures for use in swabbing fluid from an oilwell bore and more particularly involves a reinforcing structure for a swab cup and the method of manufacturing it.
Swabbing generally is the removal of liquid from a well by means of a sealing element mounted on a tool and lowered into a well by means of a wireline. The tool is lowered through a suitable amount of tubing and then lifted within the well effecting a seal with the pipe and lifting fluid above the tool to the surface. Packer cups are generally used to seal well pressure in one direction and are mounted on a well tool and positioned in a sealing engagement with well pipe. Packer cup application normally is a static or limited movement application.
There are a multitude of prior well swab bodies using a plurality of shaped wires held in base structures of various types as the reinforcing structure. See, for example, U.S. Pat. No. 2,887,347 issued to T. B. Losey. Also, see U.S. Pat. Nos. 3,724,337, 3,724,338 and 2,581,981 in which vertical reinforcing wires are clamped between two concentric base rings and an elastomeric material is bonded therearound.
There are also prior well swabs employing metallic cones or corrugated cylinders as the reinforcing structure. See, for example, U.S. Pat. Nos. 1,898,292 issued to C. S. Crickmer and 2,013,903 issued to F. A. Thaheld. There are also prior well swabs employing slotted metallic cylinders as wear protective structures. See, for example, U.S. Pat. Nos. 2,619,393 issued to R. E. Wilson and J. A. Wilson and 2,456,551 issued to R. A. Wilson.
The disadvantages of the aforementioned swabs which utilize upstanding tines or wires clamped between two concentric base rings are serious and include the particularly bothersome problem of "drift" during molding.
The normal procedure for manufacturing swab cups is to locate a complete set of reinforcing wires between two concentric base rings and then swage one or both of the rings into tight clamping arrangement with the wires. For example, the aforementioned U.S. Pat. Nos. 3,724,337 and 3,724,338 generally located the vertical wires between a hardened metal outer ring and a softer metal inner ring and then "expand" the inner ring outward to clamp the wires in place.
After the reinforcing structure is formed, it is usually then placed inside a swab cup mold and viscous elastomeric material is pressure injected into the mold to encapsulate the metal structure and fill in and around all the open spaces in the wires and base rings. The elastomer is then cured, and the cup is trimmed and is ready for use.
The difficulty encountered with this process is that the pressure injection step, involving radical thermal changes and high flow rates, tends to separate the two base rings and float them apart some distance. This results in misalignment of the upward extending wires as well as a weakening of the entire swab structure. Oftentimes, the wires will protrude through the side of the elastomeric wall and resulting in rapid wear and breakage.
In addition to this disadvantage, the hardening of the base ring is an additional step that results in greater expense and time of manufacture. This hardening is done in the prior art methods (which swage outward) in order to maintain the reinforcing cage OD within acceptable dimensional tolerances.
Disadvantages with unitary cup reinforcing structures made from tubular material are due to the time consuming machining operations and resultant high cost.
These disadvantages are ovecome by the present invention which utilizes a single U-shaped annular base cup to receive the upward tines therein and which can be swaged inward to clamp the tines tightly. Because the base is a single element, it eliminates and "drift" encountered during injection molding of the elastomer. The present invention also eliminates the need for providing a hardened metal base ring.